The present invention relates to an apparatus suitable for monitoring a respiratory gas flow, comprising a gas collector unit, which separates an ambient gas space from that remaining inside the gas collector unit, a patient respiring a gas contained in said gas collector unit, a conduit for flowing a respiratory gas from one or more gas sources into the gas collector unit to be respired by a patient, and a conduit for delivering a respiratory gas, which at least partially contains a gas exhaled by a patient, from the gas collector unit to a measuring device for examination. The invention relates also to a method suitable for monitoring a respiratory gas flow.